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Microstructured infrared sensor and method for its manufactureRelated Patent Categories: Radiant Energy, Invisible Radiant Energy Responsive Electric Signalling, Infrared ResponsiveMicrostructured infrared sensor and method for its manufacture description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060016995, Microstructured infrared sensor and method for its manufacture. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a microstructured infrared sensor and a method for its manufacture. BACKGROUND INFORMATION [0002] Microstructured infrared sensors may be used, e.g., in gas detectors, in which IR (infrared) radiation emitted by a radiation source, an incandescent bulb operated in the low-current range, or an IR LED, for example, is transmitted over a measuring path and subsequently received by the infrared sensor, and the concentration of the gases to be detected in the measuring path is estimated from the absorption of the infrared radiation in specific wavelength ranges. Gas sensors of this type may be used, e.g., in automobiles, for example, for detecting a leak in an air conditioning unit operated using CO.sub.2, or for checking the air quality of the ambient air. [0003] In general, microstructured infrared sensors have a sensor chip as a substrate in which a diaphragm, underetched by a cavity, is formed. At least one thermopile structure, having two bonded printed conductors made of different conductive materials, e.g., polycrystalline silicon and a metal, and an absorber layer for absorbing the incident IR radiation is deposited on the diaphragm. The incident IR radiation is absorbed by the absorber layer, whereupon the latter is warmed according to the intensity of the absorbed radiation. The thermal voltage across the bonded printed conductors resulting from the temperature increase is read as a measuring signal. In general, a cap chip is attached in a vacuum-tight manner to the sensor chip, whereby a sensor space shielded from the exterior is formed for the thermopile structure. The sensor may be placed into a package provided with a cover having a screen for the passage of the IR radiation. The IR radiation to be detected thus strikes the absorber layer essentially vertically after passing through the screen of the cover and the silicon cap chip which is transparent to IR radiation. The screen has approximately the same diameter as the absorber layer beneath it. [0004] To achieve sufficient sensitivity for detecting the gas concentration, a relatively large thermopile detector having a large number of thermopiles, i.e., printed conductors,,is generally formed. These may be run from the diaphragm to the surrounding substrate material in a cruciform shape. [0005] Due to the large surface area needed and the complex design of the large thermopile structures, high costs are incurred in manufacturing the infrared sensor and the sensor module made up of the sensor, the package, and the cover. [0006] An object of the present invention is to provide a method for manufacturing an infrared sensor such that a high sensitivity level is achieved for the sensor at a relatively low manufacturing cost. SUMMARY [0007] In accordance with the present invention, the incident IR radiation is focused onto the absorber layer through a convergent, i.e., convex, lens. The convergent lens is formed on top of the sensor, i.e., on top of the cap chip or a lens chip additionally attached to the cap chip, so that no additional optical aids need to be mounted and adjusted. [0008] Due to the increased sensitivity, the number of thermopiles, i.e., printed conductors, may be reduced. According to the present invention, the lateral dimensions of the diaphragm and of the absorber layer may also be reduced. [0009] The present invention utilizes the fact that when the radiation is focused onto the absorber layer by a convergent lens, a measuring signal which is proportional to the radiation may be obtained. According to the present invention, the surface of the screen may be selected to be several times larger than the screens normally used. The convergent lens is formed by the convex lens area on top of the cap chip or of the additional lens chip and the bottom of the cap chip, which may be flat, i.e., as a convex-planar convergent lens in particular. Optical focusing may be achieved here due to the difference between the refractive indices of the air inside the package and of the semiconductor material of the cap chip or of the additional lens chip, and the difference between the refractive indices of the semiconductor material and of the vacuum of the sensor space. [0010] According to the present invention, the number of thermopiles may be reduced to the point that they run only to one side of the diaphragm. [0011] According to an example embodiment of the present invention, the convex lens area on the sensor surface may be formed as a dried lacquer layer. In this case, a liquid spherical cap of an optically transparent lacquer is formed on the surface; this lacquer forms a convex shape having the desired radiation-focusing effect due to the surface tension of the liquid and the wetting of the surface. A solid spherical cap may thus be formed as a convex lens area by subsequent drying. [0012] The drop of lacquer may be formed by first applying a lacquer layer having a larger surface area and structuring a cylindrical area, which is then liquefied by inspissating a solvent. [0013] Alternatively, a liquid lacquer droplet may be directly dispensed for this purpose, e.g., via a piston dispenser having a precision needle. Time and material are saved here compared to forming and structuring the lacquer layer and inspissating solvents. The advantages of using a piston dispenser are, e.g., that changes in pressure and viscosity have no effect on the dispensed volume. Furthermore, very small volumes may be metered, volumetric reproducibility is high (e.g., .+-.2%), low-viscosity materials do not reflow, and the material is not modified by shearing. [0014] Compared to photolithography or special lithography, spin-on deposition and a prebake step of the first layer, spin-on deposition and prebake step of the second layer, edge lacquer removal, exposure, subsequent developing, and the required lacquer height control are no longer needed in the case of direct dispensing. The 10-minute dispensing step, for example, is also considerably shorter than the 45-minute swelling process required in special lithography, and the 2-hour drying, for example, according to the present invention is somewhat shorter than the 3-hour drying, for example, required for special lithography. The time for the overall process may thus be reduced by 60%, for example, and handling time by workers may be reduced by as much as over 80%. [0015] Furthermore, smaller amounts of material are used in direct dispensing, because no excess material remains at the end of the process, in contrast to a process in which layers are applied and subsequently structured. Also, no developer, no solvent for swelling, and no photoresist are required, so that a considerable additional savings in materials may also be achieved. [0016] Furthermore, in another example embodiment of the present invention, the convex lens area may also be formed in the substrate itself, i.e., in the cap chip or the additional lens chip. In this case, as in the above embodiments, a spherical cap of dried lacquer is first formed, and the spherical lacquer cap and the surrounding substrate material are then etched, e.g., dry etched. The shape of the lens formed in the substrate corresponds to the shape of the original spherical lacquer cap if the etching selectivity of the substrate material and the lacquer is selected to be 1:1; by varying the etching selectivity during the etching process, a non-spherical shape may also be achieved in the substrate, so that in principle complex geometries may also be formed. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 shows a cross-sectional view of an infrared sensor according to an example embodiment of the present invention. [0018] FIG. 2 shows a top view of a sensor chip in the diaphragm area. [0019] FIGS. 3a through 3c show the various steps of an example method for the manufacture of the cap chip of the sensor shown in FIG. 1. [0020] FIGS. 4a through 4d show the various steps of another example method for the manufacture of a lens on the cap chip. Continue reading about Microstructured infrared sensor and method for its manufacture... Full patent description for Microstructured infrared sensor and method for its manufacture Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Microstructured infrared sensor and method for its manufacture patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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